In a patient with COPD, the respiratory epithelium undergoes metaplasia. It changes from pseudostratified ciliated columnar epithelium into which type?

Correct answer: B. Stratified squamous non-keratinized epithelium

• A. Simple squamous epithelium lines alveoli and vessels — it is not the metaplastic product of chronic bronchial irritation.
• B. Correct. Chronic irritation — overwhelmingly from cigarette smoke — drives SQUAMOUS METAPLASIA: the pseudostratified ciliated columnar respiratory epithelium is replaced by STRATIFIED SQUAMOUS epithelium. The trade-off is critical: squamous epithelium is more durable against the insult but has NO CILIA and NO goblet cells, so mucociliary clearance is lost, secretions accumulate, and infection risk rises. Metaplasia is reversible if the stimulus stops; persistent injury can progress to dysplasia and carcinoma.
• C. Cuboidal epithelium is not the metaplastic endpoint in chronic airway irritation.
• D. Transitional epithelium is specific to the urinary tract.